Abstract : A preliminary experimental investigation was made of the effect of three-dimensional flow perturbations on the heat-transfer rate in the reattachment region of a laminar flow behind a two-dimensional backward-facing step. It was found that the mean value of the heat-transfer rate was increased by as much as 70% by the presence of strong flow perturbations, while the recovery factor increased approximately from the laminar value to the turbulent one. A novel technique of heat-transfer measurements was used, by which heat was uniformly dissipated on the surface of the model. A theory was developed for the case of a supersonic flow over a flat plate, which gives an exact solution of the boundary-layer equations when heat is uniformly dissipated on the surface. It was shown in particular that the ratio of the heat-transfer coefficient for an isothermal wall to the heattransfer coefficient for uniform heat-flux is a constant independent of Mach number and Reynolds number. Numerical integration showed that it is equal to 0.72, independently of the Prandtl number in the range 0.5 to 1.0. (Author)